Wiping paper is made with paper fibres and incorporates various additives including, in particular, an additive which increases its wet strength. This type of additive, which will be referred to below as a wet strength additive, forms a network through the sheet which does not affect the paper fibres' capacity to absorb liquid, whilst replacing the inter-fibre links forming the paper which are broken in the presence of water.
The fibrous and chemical composition and the structure of a paper product intended for wiping are adapted accordingly. Compared with a similar product intended for hygienic use, for example, it should have both greater tear resistance and a greater capacity to absorb liquid.
Wiping paper therefore incorporates, in chemical terms, an agent which gives it wet strength and is structured so as to absorb a maximum quantity of liquid, in particular water. To achieve this, according to prior attempts, two or more plies of embossed paper are generally combined. The embossed patterns and the deformation that they impart are selected to create the largest possible thickness whilst limiting the loss of mechanical strength caused by the embossing and resulting from the breaking of inter-fibre links along the zones which are subjected to the embossing stresses. The paper is generally creped to give it the extendability required for the embossing.
There are essentially two ways in which the plies can be assembled. The point-to-point combining method is obtained by embossing protuberances on each of the plies, separately, in the same pattern, followed by facing the protuberances of the two plies and gluing together their tops which are in contact one another. In the so-called “nested” assembly method, the two plies to be joined are embossed with protuberances that have patterns selected so that the protuberances of one ply are nested with those of the other ply, the join being made by gluing the tops of one ply to the bottom of the pattern of the other ply. With these combining methods, the absorption is thus improved compared with the base sheet owing to the spaces formed between the two plies. However, the height of the protuberances is limited by the loss of mechanical strength caused by deep embossing.
Wiping products for domestic use generally take the form of rolls with a continuous sheet in the form of a strip which may be divided into rectangular shapes by transverse pre-cuts and is wound around a core.